1. Field of the Invention
The present invention relates to a Vertical Cavity Surface Emitting Laser that includes a resonator structure radiating laser light from the top face.
2. Description of the Related Art
A Vertical Cavity Surface Emitting Laser radiates light in the direction perpendicular to the substrate differently from the existing Fabry-Perot resonator laser diodes. In the Vertical Cavity Surface Emitting Laser, many resonator structures are able to be arranged in a state of a two dimensional array on the same substrate. Therefore, the Vertical Cavity Surface Emitting Laser has recently attracted attention in the data communication field and the like.
Such a type of laser diode generally includes a resonator structure in the shape of a mesa in which a lower DBR layer, a lower spacer layer, an active layer, an upper spacer layer, an upper DBR layer, and a contact layer are layered in this order on a substrate. In one of the lower DBR layer and the upper DBR layer, to improve efficiency of current injection into the active layer and lower the threshold value current, a current confinement layer having a structure that a current injection region is confined is provided. Further, electrodes are respectively provided on the front face of the contact layer and the rear face of the substrate. In the laser diode, a current injected from the electrode is confined by the current confinement layer, and then injected into the active layer where light is emitted due to electron-hole recombination. The light is reflected by a pair of multilayer film reflectors, laser oscillation is generated in a given wavelength, and the light is radiated as laser light from the top face of the resonator structure.
In the foregoing laser diode, it is known that out of the laser light radiation region, basic transverse mode oscillation is generated mainly in the central region while high order transverse mode oscillation is generated mainly in the peripheral region. In the past, various technologies for inhibiting the high order transverse mode oscillation have been proposed. For example, in Japanese Unexamined Patent Application Publication No. 2000-332355, the following technology is disclosed. In the technology, a metal electrode having an aperture in the central region out of the laser light radiation region is provided, and reflectance in the metal electrode is decreased down to about 80% or less by alloying.